1. Field of the Invention
The present invention relates to a tightening system for tightening fastening members such as screws.
2. Description of Related Art
Conventionally, tightening systems (also referred to as “nut runners”) for tightening screws such as bolts and nuts have been used, for example, in assembly lines of automobile engines (see Japanese Patent Application Publication No. 8-11027 (JP 8-11027 A)).
Such a tightening system described above includes a drive source such as a motor, a spindle coupled to a rotational shaft of the drive source, a socket provided at a tip of the spindle, and so forth. The socket is engaged with a screw and rotated by the drive source, thus tightening the screw. Among the tightening systems, there is a system such as the tightening system disclosed in JP 8-11027 A in which the spindle is configured to be vertically moveable with respect to a workpiece. In the tightening system, when tightening a screw, the spindle having the socket moves down to the tightening positions, and moves up from the workpiece after the tightening is complete. In other words, the tightening system includes socket vertically moving means for moving the socket at the tip of the spindle up or down with respect to the workpiece by vertically moving the spindle.
A type described below has been known as one type of the socket vertically moving means. For example, in a case that the socket is positioned in the rotational axis direction of the spindle, the spindle is configured to be slidable in the rotational axis direction, and an actuator for moving the spindle allows the spindle to move forward or backward in the rotational axis direction, thereby carrying out the vertical motion of the socket at the tip of the spindle.
For example, as shown in FIG. 5, a system has been known in which a general-purpose air cylinder as the actuator is externally attached adjacent to the spindle, the spindle and a cylinder rod end of the air cylinder are coupled together by a plate, and the air cylinder extends and contracts via the plate to allow the spindle to move forward or backward, thereby vertically moving the spindle and the socket.
However, such a conventional tightening system described above uses a bulky actuator such as the air cylinder as the vertically moving means of the socket and thus becomes a large system having the actuator externally attached adjacent to a system main body. Further, when the tightening system (nut runner) becomes large as in this case, the tightening systems including a plurality of nut runners (multi-axis nut runner) may impair tightening efficiency due to the increase in interference areas among the nut runners. Accordingly, a tightening system in a further compact system configuration is desired.